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J.R., Small Engine Technician
Category: Small Engine
Satisfied Customers: 7445
Experience:  Owner of outdoor power equipment business, repairing all makes and models.
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I have a John Deere L120 lawn tractor. The PTO wont engage

Customer Question

I have a John Deere L120 lawn tractor. The PTO won't engage the mower deck. I replaced the switch (actually a knob) with a new one from John Deere. I swopped the seat switch with one from another mower that I know works. I replaced the PTO clutch. I checked the battery, its putting out 370 cca. When I engage the knob nothing happens, but if I go to reverse, the mower will engage but the the motor cuts out and the override doesn't keep it going. So the PTO does engage under that circumstance. Also, if I engage the PTO and get up off the seat again the mower engages but the motor cuts out. All wiring appears to be good and all connections also appear good.
Submitted: 6 years ago.
Category: Small Engine
Expert:  J.R. replied 6 years ago.

Do you have a voltmeter?

Customer: replied 6 years ago.
yes, I load tested the battery before bringing it in to test the c c amps. I tested fine.
Expert:  J.R. replied 6 years ago.

Have someone set on the seat. Push the clutch/brake in. Turn the key to on and then pull the pto switch out. Unplug the wires going to the pto clutch and see if you have voltage on those wires. If you have no voltage then you have a bad switch. It may be a bad ignition switch or the clutch switch since you have replaced the seat switch and the rio button.



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Customer: replied 6 years ago.
With the ignition on, motor not running, I can hear the PTO engage click when I push the seat button, and pull the PTO knob. I will check the voltage at the PTO.
Expert:  J.R. replied 6 years ago.
If it is working like that then the problem may be a bad clutch/brake pedal switch or the relay may be bad.
Customer: replied 6 years ago.
Where are they and how can I check or bypass for testing?
Expert:  J.R. replied 6 years ago.
The relay cannot be bypassed. Most of them have a diagram printed on them for testing. It should be in the main harness under the hood. The clutch switch will make contact with the shaft that the pedal is attached to. It is normally mounted on the frame.
Customer: replied 6 years ago.
I will check those things in an hour and let you know.
Expert:  J.R. replied 6 years ago.
Customer: replied 6 years ago.
Ok I checked the voltage at the wires plugged into the PTO. Motor off, key on noone on the seat. when I pull the PTO switch i get about 11.5 volts. then when someone sits in the seat the voltage drops to between 0 and 2 volts. Any thoughts
Expert:  J.R. replied 6 years ago.

It sounds like the seat switch or the relay.

Customer: replied 6 years ago.
where is the relay? I swopped the seat switch with one that works on another tractor and same problem. Then I put my seat switch in the other mower & it worked.
Expert:  J.R. replied 6 years ago.
It is a small black box. It should be located under the dash in the main wiring.
J.R. and 3 other Small Engine Specialists are ready to help you
Customer: replied 6 years ago.
I am going to replace it and I am accepting your answer, but I hope that if it doesn't fis it I can still ask you questions. Thanks!
Expert:  J.R. replied 6 years ago.
Let me know.
Customer: replied 6 years ago.
I replaced the seat switch just to be sure. I replaced the relay. I also checked voltage while running 17 volts with the seat switch not pushed. When I push the swithc voltage goes to zero. Any thoughts?
Expert:  J.R. replied 6 years ago.
It acts like you have a bad ground somewhere.

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